New demands for space and earth observations drive the need for large apertures of 10 m and higher in telescopes. This requires new types of alternative lightweight and deployable primary reflector or ... [more ▼]

New demands for space and earth observations drive the need for large apertures of 10 m and higher in telescopes. This requires new types of alternative lightweight and deployable primary reflector or lens concepts with aerial densities of\3 kg/m2. Some syntheses between optical and especially mechanical and material aspects for large planar photon sieves and non-imaging telescopes are discussed. Focus is put on large planar and highly perforated membranes for photon sieves and shell-membrane type deployable (parabolic) reflectors, respectively. The reflecting surface of the latter is composed of specific C-fiber reinforces silicone (CFRS) material. In addition to possible shape control, emphasis is also given to reflective coating of CFRS. Engineering challenges requiring future activities are identified. [less ▲]

The coarse lateral sensor is a system able to measure the lateral position between two satellites. It bridges the gap between the alignment accuracy achieved with the radio frequency metrology, and the ... [more ▼]

The coarse lateral sensor is a system able to measure the lateral position between two satellites. It bridges the gap between the alignment accuracy achieved with the radio frequency metrology, and the alignment accuracy required the highprecision optical metrology (fine-lateral and longitudinal sensor). The coarse lateral sensor developed at Centre Spatial de Liège (CSL) is a standalone unit. Once connected to an unregulated 28V power-supply, it delivers, the lateral position of a corner cube retro-reflector (within an angle of 10 arcdeg and from 25 to 250 m) and tracks this position at a rate of 10 Hz. The system is operational with the sun in its fieldof- view. Real time centroidisation algorithms allow tracking the image position and feed the on-board computer with this information via a RS422 link, allowing further position stabilization. The coarse lateral sensor has successfully undergone thermal qualification (40°C and -30 °C), and vibration test (high-level sinus, random and shock test in the 3– axis). [less ▲]

The lateral sensor is a system able to measure the lateral position between two satellites. It bridges the gap between the alignment accuracy achieved with the radio frequency metrology, and the alignment ... [more ▼]

The lateral sensor is a system able to measure the lateral position between two satellites. It bridges the gap between the alignment accuracy achieved with the radio frequency metrology, and the alignment accuracy required to start the high-precision optical metrology (fine-lateral and longitudinal sensor). This project concerns the demonstration of formation flying technologies for future European scientific and application missions of the EUROPEAN SPACE AGENCY. Technological developments enabling formation flying have already been initiated and some precursor missions already cover part of the related technologies, for example SMART-2. The lateral sensor developed at Centre Spatial de Liège (CSL) is based on a camera (CMOS detector) a telecentric lens designed at CSL, a fibre-coupled laser-diode bar and a corner cube. The fibre-coupled laser-diode bar emits a diverging beam, from the master spacecraft to a slave spacecraft. A corner cube located on the slave spacecraft sends the light back. This light is captured by the telecentric lens and camera (build by Deltatec Liège-B). A lateral shift “d” of the corner cube is seen on the camera as an image displacement. Real time centroidisation algorithms will allow tracking the image position and feed the on-board computer with this information via a RS422 link, allowing further position stabilisation. The imaging system needs to operate in a depth of field from 25 m to 250 m. Because of the large depth of operation, all lateral system performances are angular ones. The system is build to meet: • Tracking capability for a spot moving @ 0.5 arcdeg/sec • Spot detection with the sun in the field of view • Centroidisation accuracy: 0.1 camera pixels (3.5 arcsec) • Absolute calibration accuracy: 0.14 camera pixels (5 arcsec) In order to comply with these requirements, the following features were implemented : • The camera allows quick read-out of sub-windows of interest (in 1 ms). • Optimize radiometric budget and laser diode power consumption, and its related heat dissipation. • An interference filter blocks all unwanted light centred on the laser wavelength (980 nm). • The detector captures the images. An electronic unit records the images and localizes the bright spot (return image from the corner cube). • Implementation of a “slow detection mode”, which allows to discriminate sun from moving image The system is a standalone unit. Once connected to an unregulated 28V power-supply, it delivers, after spot detection, pixel coordinates to the RS422 link at a 10 Hz rate. Its average power consumption is 8W. The system can be put in a programming mode, to allow uploading settings in the FPGA. Tracking, absolute calibration, resolution and sun avoidance have been measured in a field of 10 arcdeg and the range of depth of 5 m to 80 m. The coarse lateral sensor has successfully undergone thermal qualification (40°C and -30 °C), and vibration test (high-level sinus, random and shock test in the 3–axis). Its metrology performances (centroidisation accuracy (<0.1 pixel RMS) and tracking) remained unchanged after these qualification tests. The absolute calibration is 0.3% in the interval of ±5arcdeg (11 arcsec in ±1arcdeg). [less ▲]

Videogrammetry is a 3-dimensional co-ordinate measuring technique that (now) uses digital image capture as the recording method. Images are taken from at least two different locations and the light-rays ... [more ▼]

Videogrammetry is a 3-dimensional co-ordinate measuring technique that (now) uses digital image capture as the recording method. Images are taken from at least two different locations and the light-rays from the camera to the measurement object are intersected by triangulation into 3D point coordinates. With a large number of images, the camera orientation and 3D point locations are accurately determined with the use of a full mathematical model (bundle adjustment). Adhesive targets are commonly used for point materialization. Those targets consist of a retro-reflective material, with an adhesive backing for sticking to the structure under investigation. A drawback of these types of targets is that they can lose their adhesion and shape during thermal vacuum cycling, especially when cryogenic temperatures are involved. In addition the operation of placing and removing targets is a critical procedure that can lead to undesirable contamination and damage to the test item. Because they require to be physically attached to the surface to be measured, this can also compromise the quality assurance of the test object. Such problems were encountered during cryogenic thermal vacuum qualification testing of the ESA Planck Surveyor mission telescope reflectors. In the development described here the aim was to replace the use of adhesive targets by projected dots. The idea is not fundamentally new. Indeed a US company, Geodetic Systems Inc. (GSI) proposes already a commercial target projector for videogrammetry which uses a flashlamp and is adequate for workshop and laboratory applications. Dot projection videogrammetry is also suggested as a shape measurement method of Gossamer structures, membrane reflectors, etc…Note that there are fundamental differences in use and applications of retro-reflective targets and dot projection: • Retro-reflective targets are materialized on the test article. They appear as fiducials attached to the test article. Any relative distortion of the materialized point can be tracked with respect to the test article itself. • Projected dots are not materialized on the object. Practically a specific point cannot be tracked by this method. The dense cloud of projected dots allows sampling the surface or the shape in an arbitrary way.The Target Projector System (TPS), described here (Fig.1), was designed and manufactured to operate in the Large Space Simulator (LSS) of ESAof ESA under thermal vacuum conditions and to have a minimized temperature exchange with its environment. It is operational over a temperature range of 90K to 350 K, and has a wavelength of 808 nm.Qualification tests and results under vacuum, along with an assessment of the videogrammetric accuracy achievable for various configurations of this unique device are presented. [less ▲]

The European Space Agency ESA aspires the exploration of the universe using space-borne infrared telescopes with large aperture operating at cryogenic temperature. The Herschel space telescope is ... [more ▼]

The European Space Agency ESA aspires the exploration of the universe using space-borne infrared telescopes with large aperture operating at cryogenic temperature. The Herschel space telescope is currently returning its first scientific observations orbiting from the Lagrange point L2 and the foreseen infrared observatory Spica is currently under study. The large diameter of the primary mirrors and the operation at cryogenic temperature require the use of ultra stable materials and wellcharacterised dimensional change of the structure as function of temperature. Dimensional stability and high precision data on the thermal expansion is also relevant for the cryogenic spectographs MIRI and NIRspec on the James Webb Space Telescope JWST, for high-precision laser interferometer LISA and for spacecraft sent to a hot environment such as BepiColombo and Solar Orbiter. Although European industry has proven effective at designing and building thermally stable structures, problems have been encountered in measuring the absolute CTE of stable materials. In one recent mission, the design CTE had to be changed 6 times over a 2 year period and when the telescope was tested in cryogenic conditions, an error was found in the back focal plane of over a centimetre. It is an objective of ESA to determine the CTE of stable materials continuously as function of temperature with an uncertainty of 3 ppb/K down to a temperature of 5 K. [less ▲]

Nowadays spaceborne missions for astronomy or Earth imaging need high resolution observation which implies the development of large aperture telescopes. This can be achieved by multi-aperture telescopes ... [more ▼]

Nowadays spaceborne missions for astronomy or Earth imaging need high resolution observation which implies the development of large aperture telescopes. This can be achieved by multi-aperture telescopes or large segmented telescopes. One of the major issues is the phasing of the sub-apertures or the segments of such telescopes. A cophasing sensor is therefore mandatory to achieve the ultimate resolution of these telescopes. In this framework, Liège Space Center (CSL) concern is the development of a compact cophasing sensor to phase new large lightweight segmented mirrors for future space telescopes. The sensor concept has its origins in new phase retrieval algorithms which have been recently developed. In this paper, we outline the concept and the experimental validation results of our piston sensor breadboard which is currently under development in our laboratory. Finally, future prospects and further developments of our experiment are presented. [less ▲]

The European Space Agency’s Planck satellite, launched on 14 May 2009, is the third-generation space experiment in the field of cosmic microwave background (CMB) research. It will image the anisotropies ... [more ▼]

The European Space Agency’s Planck satellite, launched on 14 May 2009, is the third-generation space experiment in the field of cosmic microwave background (CMB) research. It will image the anisotropies of the CMB over the whole sky, with unprecedented sensitivity ( ΔT T ∼ 2 × 10−6) and angular resolution (∼5 arcmin). Planck will provide a major source of information relevant to many fundamental cosmological problems and will test current theories of the early evolution of the Universe and the origin of structure. It will also address a wide range of areas of astrophysical research related to the Milky Way as well as external galaxies and clusters of galaxies. The ability of Planck to measure polarization across a wide frequency range (30−350 GHz), with high precision and accuracy, and over the whole sky, will provide unique insight, not only into specific cosmological questions, but also into the properties of the interstellar medium. This paper is part of a series which describes the technical capabilities of the Planck scientific payload. It is based on the knowledge gathered during the on-ground calibration campaigns of the major subsystems, principally its telescope and its two scientific instruments, and of tests at fully integrated satellite level. It represents the best estimate before launch of the technical performance that the satellite and its payload will achieve in flight. In this paper, we summarise the main elements of the payload performance, which is described in detail in the accompanying papers. In addition, we describe the satellite performance elements which are most relevant for science, and provide an overview of the plans for scientific operations and data analysis. [less ▲]

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2009), 3(48),

This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation. The mirror ... [more ▼]

This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation. The mirror may be used on its own, or as a segment of a larger mirror. The typical size of one segment is 100to200mm ; the production process relies on silicon wafers and thick film piezoelectric material deposition technology; it is able to lead to an actuation pitch of the order of 5mm , and the manufacturing costs appear to grow only slowly with the number of degrees of freedom in the adaptive optics. [less ▲]

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film ... [more ▼]

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film membranes. Their inherent properties (low mass and small thickness) preclude the use of conventional measurement methods (accelerometers and displacement transducers for example) during on-ground testing. In this context, innovative non-contact measurement methods need to be investigated for these stretched membranes. The object of the present project is to review existing measurement systems capable of measuring characteristics of membrane space-structures such as: dot-projection videogrammetry (static measurements), stereo-correlation (dynamic and static measurements), fringe projection (wrinkles) and 3D laser scanning vibrometry (dynamic measurements). Therefore, minimum requirements were given for the study in order to have representative test articles covering a wide range of applications. We present test results obtained with the different methods on our test articles. [less ▲]

This paper addresses the interferometric measurements performed on PLANCK Secondary reflector-Flight Model (SRFM) during the cryo-optical test at the Centre Spatial de Liege in Belgium. It was requested ... [more ▼]

This paper addresses the interferometric measurements performed on PLANCK Secondary reflector-Flight Model (SRFM) during the cryo-optical test at the Centre Spatial de Liege in Belgium. It was requested to measure the changes of the surface figure error (SFE) with respect to the best ellipsoid, between 293 K and 50 K, with a 1 μm RMS accuracy. To achieve this, Infra Red interferometry has been selected and a dedicated thermo mechanical set-up has been constructed. One emphasizes on the solutions adopted to cope with high surface slopes appearing at cryogenic temperature. Indeed, detector resolution has been exploited to resolve high density fringes at the expense of the aperture. A stitching procedure has been implemented to reconstruct the full aperture measurement with success. Test results are presented. [less ▲]

A breadboard set-up has demonstrated a concept of co-phasing and co-alignment based on an external reference source for synthetic aperture telescopes applications. These types of systems can be extremely ... [more ▼]

A breadboard set-up has demonstrated a concept of co-phasing and co-alignment based on an external reference source for synthetic aperture telescopes applications. These types of systems can be extremely valuable in order to perform coarse re-alignment of synthetic aperture telescope, following thermo-elastic deformation and deployment effects in space flight environments. [less ▲]

The cryo-optical testing of the PLANCK primary reflector (elliptical off-axis CFRP reflector of 1550 mm x 1890 mm) is one of the major issue in the payload development program. It is requested to measure ... [more ▼]

The cryo-optical testing of the PLANCK primary reflector (elliptical off-axis CFRP reflector of 1550 mm x 1890 mm) is one of the major issue in the payload development program. It is requested to measure the changes of the Surface Figure Error (SFE) with respect to the best ellipsoid, between 293 K and 50 K, with a 1 μm RMS accuracy. To achieve this, Infra Red interferometry has been used and a dedicated thermo mechanical set-up has been constructed. This paper summarises the test activities, the test methods and results on the PLANCK Primary Reflector - Flight Model (PRFM) achieved in FOCAL 6.5 at Centre Spatial de Liege (CSL). Here, the Wave Front Error (WFE) will be considered, the SFE can be derived from the WFE measurement. After a brief introduction, the first part deals with the general test description. The thermo-elastic deformations will be addressed: the surface deformation in the medium frequency range (spatial wavelength down to 60 mm) and core-cell dimpling. [less ▲]

in Osten, W.; Novak, E. (Eds.) Proceedings of the Eighth International Conference on Laser and Laser Information Technologies (2004, August 02)

In the frame of cryogenic test on an off axis ellipsoid, it has been required to set-up an unambiguous method to determine and track the foci position during temperature transitions. This procedure was ... [more ▼]

In the frame of cryogenic test on an off axis ellipsoid, it has been required to set-up an unambiguous method to determine and track the foci position during temperature transitions. This procedure was mandatory to avoid: (1) impact of the operator skills working on triple shift scheme to assure continuously monitoring of the ellipsoid shape during cool down. (2) correctly dissociate the impact of the thermal deformation on the mirror shape with respect to alignment errors. This paper will demonstrate the process, starting from ideal ellipsoid shape, then introducing 3D metrology data in a model, and finally presents the results in a practical situation. [less ▲]

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. Scientific ... [more ▼]

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. Scientific observatories require large telescopes with precisely shaped reflectors for collecting the electro-magnetic radiation from faint sources. The challenging tasks of on-ground testing are to achieve the required accuracy in the measurement of the reflector shapes and antenna structures and to verify their performance under simulated space conditions (vacuum, low temperatures). Due to the specific surface characteristics of reflectors operating in these spectral regions, standard optical metrology methods employed in the visible spectrum do not provide useful measurement results. The current state-of-the-art commercial metrology systems are not able to measure these types of reflectors because they have to face the measurement of shape and waviness over relatively large areas with a large deformation dynamic range and encompassing a wide range of spatial frequencies. 3-D metrology (tactile coordinate measurement) machines are generally used during the manufacturing process. Unfortunately, these instruments cannot be used in the operational environmental conditions of the reflector. The application of standard visible wavelength interferometric methods is very limited or impossible due to the large relative surface roughnesses involved. A small number of infrared interferometers have been commercially developed over the last 10 years but their applications have also been limited due to poor dynamic range and the restricted spatial resolution of their detectors. These restrictions affect also the surface error slopes that can be captured and makes their application to surfaces manufactured using CRFP honeycomb technologies rather difficult or impossible. It has therefore been considered essential, from the viewpoint of supporting future ESA exploration missions, to develop and realise suitable verification tools based on infrared interferometry and other optical techniques for testing large reflector structures, telescope configurations and their performances under simulated space conditions. The first one is an IR-phase shifting interferometer with high spatial resolution. This interferometer shall be used specifically for the verification of high precision IR, FIR and sub-mm reflector surfaces and telescopes under both ambient and thermal vacuum conditions. The second one presented hereafter is a holographic method for relative shape measurement. The holographic solution proposed makes use of a home built vacuum compatible holographic camera that allows displacement measurements from typically 20 nanometres to 25 microns in one shot. An iterative process allows the measurement of a total of up to several mm of deformation. Uniquely the system is designed to measure both specular and diffuse surfaces. [less ▲]

in Warmbein, B. (Ed.) Proceedings of the 5th International Conference on Space Optics (ICSO) (2004, April 02)

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. The ... [more ▼]

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. The challenging tasks of on-ground testing are to achieve the required accuracy in the measurement of the reflector shapes and antenna structures and to verify their performance under simulated space conditions (vacuum, low temperatures). A small number of infrared interferometers have been commercially developed over the last 10 years but their applications have also been limited due to poor dynamic range and the restricted spatial resolution of their detectors. It has therefore been considered essential, from the viewpoint of supporting future ESA exploration missions, to develop and realise suitable verification tools based on infrared interferometry and other optical techniques for testing large reflector structures, telescope configurations and their performances under simulated space conditions. Two methods and techniques are developed at CSL. The first one is an IR-phase shifting interferometer with high spatial resolution. This interferometer shall be used specifically for the verification of high precision IR, FIR and sub-mm reflector surfaces and telescopes under both ambient and thermal vacuum conditions. The second one presented hereafter is a holographic method for relative shape measurement. The holographic solution proposed makes use of a home built vacuum compatible holographic camera that allows displacement measurements from typically 20 nanometres to 25 microns in one shot. An iterative process allows the measurement of a total of up to several mm of deformation. Uniquely the system is designed to measure both specular and diffuse surfaces [less ▲]

in Decker, J.; Brown, N. (Eds.) Proceedings of the Conference on Recent Developments in Traceable Dimensional Measurements, (2003, November 20)

The development of a canister-free videogrammetry system is presented. Applications in view, are coordinate measurements during thermal vacuum test and on-baord space flight metrology of mechanical ... [more ▼]

The development of a canister-free videogrammetry system is presented. Applications in view, are coordinate measurements during thermal vacuum test and on-baord space flight metrology of mechanical structures, reflectors and antenna's. The paper presents the breadboard system architecture. Two breadboards have been developed. One is based on a space-qualified micro-imager camera. Lenses and flashers are all commercial components and have been made vacuum compatible. Results of accuracy (typically 50ppm) and resolution (typically 25 ppm) tests, in ambient and in vacuum are also presented. [less ▲]

PLANCK is the third Medium size mission of the ESA long-term scientific plan Horizon 2000. This paper present the current design status of the design of the cryo-optical test for the Planck primary ... [more ▼]

PLANCK is the third Medium size mission of the ESA long-term scientific plan Horizon 2000. This paper present the current design status of the design of the cryo-optical test for the Planck primary reflector and Planck secondary reflector [less ▲]